1. The Field of the Invention
This invention relates generally to touchpad technology. Specifically, the invention is an improved system and apparatus for utilizing a touchpad which is primarily used for cursor control on a computer display. The advantages of the invention relate generally to improved noise rejection, immunity to the effects of moisture on the touchpad surface, increased manufacturing tolerances, an improved scanning pattern, and an adaptive motion filter.
2. The State of the Art
The state of the art in capacitance sensitive touchpad technology spans a variety of different technologies and methodologies for sensing the location and movement of a pointing object as it moves across a touchpad surface. The means by which data can be input to a computer or other electronic apparatus are many. For example, one method of providing input is through manipulation of a cursor on a computer display. By controlling a cursor, the cursor can be caused to move icons or other objects on the display, such as text, or select buttons, hyperlinks or icons. In addition, discrete tappings on the touchpad surface can be caused to actuate buttons or controls that are disposed beneath the cursor on the computer display. Another method of data input includes using gestures that can be recognized by programming routines disposed in the software or firmware of the touchpad.
However, regardless of whether the touchpad is being used for cursor control or any of the other methods of data input, touchpads are being called upon to be more versatile, and to operate more reliably, especially in adverse operating conditions and environments.
The demands of data input reliability are especially becoming more critical. Touchpads are not only being used in many portable computers, but also in personal information managers (PIMs) and personal digital assistants (PDAs). The desire to be mobile and at the same time connected to communications services has consequently created the need for novel forms of data input. But new applications for the use of touchpads have brought more challenges for reliable performance. These challenges not only come from the devices in which they are used, but the environments in which they operate as well.
For example, moisture on a touchpad surface has always been a hindrance to reliable touchpad operation. But touchpads are not only being used in very humid climates, but also in inclement weather, where water droplets might splash onto the touchpad surface. State of the art touchpads perform poorly in these situations, again posing challenges to reliable touchpad performance.
Weather and climate are not the only formidable problems for touchpads. For example, the electronic environment poses its own kind of challenges. Consider a portable computer that is operating on its own internal battery power supply. The user might want to save battery power by plugging into an AC outlet. The electronic noise generated by an AC power source is very large, and can significantly impact the performance of a touchpad.
Another problem in the state of the art is inevitable when the touchpad is being used in a portable device. Power consumption will always be an issue when operating away from an AC or large DC power source. However, touchpad circuitry has generally not been considered an area where power usage can be minimized. Nevertheless, it has been determined by the inventors that significant improvements in power conservation can be obtained.
Accordingly, what is needed is an improved touchpad that is able to compensate for general electromagnetic noise (EMI) interference, as well as the more specific problems of noise from an AC power source. It would also be an improvement to have increased immunity to the problems created for a touchpad when exposed to moisture and water droplets.
Along with the noise and moisture problems identified above, there are other problems more general to touchpad performance. For example, manufacturing tolerances of the sensing circuitry are not very forgiving in the state of the art. The result is that touchpads have required precision layout of sensor electrodes. Without precision layout, the sensing circuitry is not capable of compensating for variations in the layout. Thus, manufacturers have often had to use more costly PC boards to obtain the precise layout needed for reliable touchpad operation.
Accordingly, it would be an improvement over the prior art to improve the performance of the sensing circuitry such that the circuitry could tolerate and compensate for greater variations in the layout of the sensing electrodes. This can be accomplished by improving the dynamic range of the sensing circuitry.
Another problem inherent to touchpads is locating a valid object on the touchpad surface. The total number of measurements of the sensing circuitry that are required to locate the valid object has a significant affect on power consumption. Accordingly, it would an improvement over the prior art to have quicker scanning algorithms, thereby enabling the sensor circuitry to power down and thereby conserve power. It would also be an advantage over the prior art to be able to compensate for objects which are no longer considered to be valid objects on the touchpad surface.
Another reliability issue of touchpads lies in the sensing circuitry. The prior art generally scans for objects with a single algorithm. In other words, there are no adjustments made in scanning routines for objects that are moving rapidly or slowly.
It would be an improvement over the prior art to utilize an adaptive motion filter which can compensate for the speed at which an object on the touchpad surface is moving. The advantage of this type of filtering is that the touchpad is capable of more precise sensing when the object is moving slowly, and keep pace with an object that is moving faster by using reduced filtering. Effectively, the resolution is decreased in exchange for keeping pace with the object being tracked.
A last performance issue of prior art touchpads is concerned with the sampling of data from the sensing electrodes. Noise in the touchpad circuitry can prevent the sensing circuitry from performing correctly.
Therefore, it would be an advantage over the state of the art in touchpads to provide a filter which could compensate for noise and prevent false signals from affecting location calculations of the touchpad.